Free

Free software is not free - it comes with an implicit obligation that you respect the rights of its creators, and that you give something back from your use of the software, from code libraries to promotion to documentation, to the larger community. It's possible, indeed probable, that this ethos, derived by programmers and engineers to solve some very real problems, may in fact be a sound model on which to build an economy.

Cagle, Kurt. O'Reilly and Associates (2009). Articles>Publishing>Writing>Micropayments